i have an application that sends out mails through a user account. but recently the mails sent out by this application does not get to the recipients except when manually sent (i mean using another user account). from message tracking this is what i get:

Featured Links*

The last line of your Message Tracking log indicates the message left Exchange. Next look at your SMTP log to see if the transmission succeeded or failed. You can also look in your queues to see if the message is retrying.

I suggest either enabling SMTP logging (at least long enough to help troubleshoot), downloading/running the Exchange Troubleshooting Assistant (ExTRA) from Microsoft, and/or testing connectivity using a Telnet session.

This line: smtp: message transferred to **************** through SMTP.

Means that the server the message was sent to was behind a Cisco PIX. Message tracking shows exactly what is in the SMTP banner. Therefore if the server says 220 Welcome then message tracking would say smtp: message transferred to Welcome through SMTP

My instinct is that the recipient server is blocking or dropping the messages, but while they have FIXUP SMTP enabled on their PIX you cannot know whether it is being delivered to their server correctly. Is this happening with other recipients?

If it is just this recipient then the PIX is the prime candidate as the cause of the problem. It is notorious for causing these issues. It is a problem with the FIXUP SMTP option on the PIX. If the recipient will not turn off the FIXUP SMTP option then you will have to send email for that recipient via your ISP.